The present invention relates to a matrix display control process. It is more particularly used in the construction of liquid crystal display devices, used more especially in the binary display of complex images or alphanumeric characters.
These matrix display devices are generally constituted by a material formed from several areas distributed in matrix-like manner and intercalated into a cross-bar system. Such systems comprise a first group of p rows of parallel electrodes and a second group of q columns of parallel electrodes, the electrode rows and columns crossing one another, an area ij of the material being defined by the overlap region between row i, in which i is an integer such that 1.ltoreq.i.ltoreq.p and by the column j, in which j is an integer such that 1.ltoreq.j.ltoreq.q. These systems also comprise means making it possible to supply appropriate excitation signals on the electrode rows and columns and which are used for exciting an optical property of the material.
Numerous devices of this type are known, which e.g. use as the sensitive material, a liquid crystal film and in which the excitation is of an electrical nature. The invention is more particularly applicable to such devices, but more generally applies to any device incorporating a material, whereof an optical property can be modified with the aid of a random excitation. This excitation can be of an electrical nature, such as for liquid, crystals, but can also be of a magnetic, thermal, electronic, or similar type. The material can be an amorphous or crystalline liquid or solid body. The optical property can be an opacity, a refractive index, a transparency, an absorption, a diffusion, a diffraction, a convergence, a rotary power, a birefringence, a reflected intensity in a given solid angle, etc.
The most commonly used liquid crystal matrix display control process consists, e.g., of sequentially or successively applying an electrode rows, sinusoidal electrical signal S.sub.o and applying in parallel or simultaneously on electrode columns and during the addressing of a row, sinusoidal electrical S.sub.j, which can either be in phase opposition, or in phase with the signal S.sub.o, depending on whether or not it is wished to display the corresponding liquid crystal area.
FIG. 1 shows an example of signals applied to the electrode rows and to the electrode columns of a matrix display or imager. The first signal a, corresponds to the signal applied in row i, the second signal b corresponds to the signal applied on column j and the third signal c corresponds to the signal or voltage, seen by area ij of the display material. Time T corresponds to the time during which row i and column j are addressed and time t to the time containing the information necessary for the display or non-display of material area ij. For a sequential addressing of the p rows, time T corresponds to the addressing time of all the rows and is governed by equation T=pt.
This control process, which is easy to perform, can only be used for a limited number of rows (p close to 100), which limits its use. Thus, in certain applications such as in pocket televisions, text display screens, etc., the number of rows required is very large to enable the use of said control process. The use of this process leads to an inadequate contrast between the displayed points and the undisplayed points, so that a blurred image is obtained. This is linked with the reaction time of the display material during its excitation and/or to its memory effect.
For these applications, it is necessary to use electrode structures and control signals making it possible to retain the number of display points or display areas which are desired on the display or imager and divide by two the number of sequentially addressed electrode rows.
One of the solutions consists of using electrode columns with a special geometry permitting the parallel control thereof, as well as the simultaneous control of the electrode row i and the electrode row i+1. This solution developed by Itachi was decribed at the conference of the "Society for Information Display" in 1980. This solution is compatible with taking information on a video signal, with storage with respect to the row. Unfortunately, the structure of the electrode columns is complex and their realisation difficult.